Such apparatus is referred to technically as a "between the shafts packing". It serves, among other things, to separate rotor regions from one another with minimum leakage losses, the rotor regions containing the same or different fluids, for example, gas/gas or gas/oil in turbo-engines, such as gas turbine power plants. In multi-shaft gas turbine jet engines, hollow shafts are used, for example, for conducting turbine cooling air, bearing chamber barrier air, rotor-stator barrier sealing air or deicing air which has been branched off from the compressor. In this regard, for example, the branched-off air must frequently be fed from an outer shaft to an inner shaft and then back out from the inner shaft. Rotor sections are used in which rotating shafts overlap one another and the branched-off air must be capable of being conducted with minimum leakage within the associated path at the operating pressure and velocity in order not to impair the aerothermodynamic cyclic process of the engine and to prevent possible mechanical damage to the power plants especially the bearings.
Sealing apparatus for the above use is known in which labyrinth seals, radially wiping seals and axial/radial sliding-ring seals are utilized.
Improvements in such sealing apparatus have been sought to minimize susceptibility of leakage and wear especially at high shaft speeds and temperatures but these have led to complex constructions which are susceptible to breakdown and are difficult to assemble. Furthermore, the improvements frequently didn't accommodate relative axial displacements of the shafts.
This is particularly of labyrinth seals which require a comparatively precise adaptation of the ends of the sealing numbers which engage in interdigitated manner with each other, in order to achieve improvements with respect to the susceptibility to leakage.
Radial wiping seals permit limited relative axial displacements between two shafts but, in general, cannot handle relatively high shaft speeds of rotation and are comparatively difficult to assemble since a leather or rubber-like packing ring is forced, by means of a special tool, with plastic deformation, into an undercut arrangement in a correspondingly preshaped cutout in the housing and then must be secured in place as well as coaxially coupled to the shaft by a coaxial connecting spring.
An essential disadvantage of the axial/radial planar ring seal is the necessity of using slit packing rings and the additional points of leakage which are thus formed. Furthermore, problems arise from this type of sealing apparatus with respect to the required run-in precision and the wear on the axial alide surface, which applies in similar manner also, for example, to pure axial sliding ring seals.
Also known are gas or hydrodynamically operating sliding ring seals between the rotor and stator of a corresponding turbo-engine which, in order to minimize the wear of corresponding radial sealing surfaces, require a lubrication sealing clearance construction which is controlled fluidly or thermally. The sealing apparatus requires the formation of lubricant application pockets along the sliding surfaces and peripheral cooling channels in the rotating sealing ring which makes such sealing apparatus comparatively difficult to construct and expensive.